National's opponents beware. This week's shock sackings of Phil Heatley and Kate Wilkinson from the Cabinet provided instant and ample proof of one surefire thing: the authentic version of John Key is back and very much in charge. The Prime Minister most definitely means business in 2013.

Utterly unapologetic about axing steadfastly loyal colleagues, Key displayed no discernible symptoms redolent of the occasionally out-of-sorts, at times seemingly indifferent and abnormally memory-challenged character who occupied Premier House through 2012.

This week witnessed the return of the composed, confident, communicative and assertive Key who, before last year's string of calamities, had carried all before him.

At times during 2012 - particularly with regard to his and his officials' farcical stumbling over Kim Dotcom - Key seemed to be playing something akin to Russian roulette with his prime ministership.

He seemed to deliberately dig himself into ever deeper political holes in order to test his wherewithal in extracting himself from them.

The conclusion drawn from this ultimately self-destructive behaviour was that he was bored or tiring of the job and its unrelenting demands.

That would no longer seem to be the case. This week's Cabinet reshuffle was clearly the product of some considerable thought over the summer break by Key and his advisers.

There was a sharp intake of breath by journalists at Tuesday's press conference as they realised the expected minimalist reshuffle necessitated by the change in Parliament's Speaker was something more akin to a Night of the Long Knives.

Heatley and Wilkinson never saw the axe coming. But then there was no reason for them to be wary.

Even a Prime Minister as openly scornful and mocking of ministerial incompetence as Helen Clark never sacked anyone for failing to do their job for fear she would make unnecessary enemies.

While hardly setting the world on fire, neither Heatley nor Wilkinson was making a mess of their respective portfolios.

Unlike Hekia Parata. The Education Minister, however, has an important ally in Bill English. Key has also invested a fair amount of political capital in her ultimately being a success in her extremely challenging portfolio.

The highly dysfunctional and teacher union-driven Ministry of Education has instead become the scapegoat within National for her mistakes. Add the dynamic of Parata being one of the few high-ranking Maori within National and it becomes clear why she survived.

Amazingly, Heatley, at least publicly, bought Key's story that he had to be fired because it was the duty of the leader to refresh his Cabinet and keep the party rejuvenated.

That is true to some extent. Key could have continued with the same line-up and kept his fingers crossed that a reasonable quota of ministers would signal their retirements as the next election edged closer.

That happened in sufficient numbers in 2011. It seems unlikely to occur in 2014, however.

With 32 of his 59 MPs without a formal role other than chairing a select committee - and only a handful of them lucky enough to enjoy that status - Key had to signal to his back bench that promotion to the Executive was still a possibility.

Tossing Heatley and Wilkinson on the political scrapheap with such alacrity has set a surprising, though long overdue precedent in terms of flouting the normal conventions of loyalty. But the pair's departure was also absolutely vital in giving the reshuffle real cut-through.

In one stroke, Key showed he has returned from his holiday energised, engaged and focused and impatient for his Government to make progress on some pressing issues.

The mid-term year of the electoral cycle is seen by Key as critical in determining National's likelihood of winning a third term in power.

Voters may wait until election year, the election campaign and even the week before polling day to finally make up their minds. But their thinking about which way they will go will start to crystallise this year.

Almost subconsciously, voters will thus be assessing whether National still has something to offer or whether the Government is running out of steam.

The reshuffle was designed to inject a new sense of urgency into the Government which Key hopes will be picked up by the public.

Maintaining momentum - or at least the appearance of it - is crucial.

National accordingly cannot afford a repeat of the string of distractions and sideshows which dominated politics in 2012 and which made the Government look as though it was bogged down by the trivial and the irrelevant.

As it is, second-term governments are always fighting against a natural erosion of support.

In Key's case, he is also fighting an Opposition which is starting to benefit from issues it can fight on its terms, rather than on National's.

In particular, Labour is winning the argument about housing affordability. National can try to persuade people that Labour's bold plan to build 100,000 homes over 10 years at a cost of $300,000 each is not feasible in Auckland where section prices are through the roof. The pulling power of Labour's scheme is that while people may question the credibility of its component parts, they want to believe it can happen.

National's other Achilles heel is jobs. Key knows that only one indicator matters - the unemployment level recorded by Statistics New Zealand's household labour force survey.

National is likely to invest considerable effort in policies aimed at driving that figure lower.

On that score, Key's economic scene-setter speech in Auckland yesterday focused on the need to attract investment - local or foreign - as the necessary precursor to creating jobs.

National's argument is that while Labour and the Greens talk about investment creating jobs, those two parties do their utmost to block it.

Key also cheekily flagged significant alterations to the modern apprenticeship scheme. Labour views the scheme as very much its territory. Key's speech was thus designed to spike at least part of David Shearer's address tomorrow to Labour's annual summer school.

Like Key, Labour's leader had sought to get his political year off to a flying start. The latter also views the mid-term year as the critical time to make Labour relevant again to a wider cross-section of voters than was the case in 2011.

But - as yesterday's announcement by Key on apprenticeships showed - National has one advantage. As one Beehive staffer puts it: Governments can do things. Oppositions can only talk of doing things.

Expect National to be doing lots of things this year. One thing is for sure: the unhappy fate of Heatley and Wilkinson serves as a gruesome reminder to the rest of the Cabinet of what will happen to ministers who do not pull their weight.

Herald political correspondent John Armstrong has been covering politics at a national level for nearly 30 years.
Based in the Press Gallery at Parliament in Wellington, John has worked for the Herald since 1987.
John was named Best Columnist at the 2013 Canon Media Awards and was a previous winner of Qantas media awards as best political columnist.
Prior to joining the Herald, John worked at Parliament for the New Zealand Press Association. A graduate of Canterbury University's journalism school, John began his career in journalism in 1981 on the Christchurch Star. John has a Masters of Arts degree in political science from Canterbury.